Hi, I have True T49F. When I plug in the system runs, but the evap fans was run. Then for a minute the Compressor frost up. So what do I need to check? Please help......

This could be a sign that it is low on refrigerant. If it is a cap tube system, this is usually an indication of the issue. I would start there. Also, be sure that the evap fan is running as it will cause frosting as well.

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The fan should run when the compressor runs.

sounds like the compressor is not running. The condenser fans are located at the compressor. The fans in the conditioned space are the evap fans. A refrig usually does not have any device controlling the evap fans, they are to run 24/7. Freezers have other controls. Start there and let me know if I can help further.

Look to the fan delay/defrost terminator that is located inside to the evap. It is usually attached to the evap coil. check there first.

Probably the compressor has shorted.
99.999% of the time this is the main culprit.
Otherwise wiring short.

Is there anything obstructing the fan area, ice build up ? It is normal for your freezer to get warm if evap fan is not working, it is essential for it to work :) A defrost cycle should kick on a timer or as needed (adaptive) and there should not be excessive frost buildup that it blocks your evap fan. I would have suggested you unplug your refrigerator for about 10 minutes and see if that resets your control board - if not, then you will need service - either replacing motor assembly or a faulty control board.

Freezers have a sensor that is referred to as a "Fan Delay/Defrost Terminator". It senses the temp during the defrost cycle. Usually, when the evap temp reaches about 50 degrees, there should not be any frost or ice on it. This device terminates the defrost cycle. It also keeps the fans off so warm air is not circulated. When the evap gets to about 20 degress or so, the sensor switches on the evap fans. If the fans are not coming on, either the sensor is bad or the evap is not reaching the proper temp to cause the sensor to turn on the fans.

Hope is helps to clear up some things and point you in a direction as to what might be going on.

Most all commercial freezers have some sort of fan delay/ defrost termination device. Commonly called a "Klixon" (pronounced clicks-on). It is a device that is attached to the evap. It's function is to terminate the defrost cycle when the evap reaches a certain temp, say about 50 degrees or so, to ensure there is no build up of frost/ ice on the evap. It then allows the compressor to run, and cool the evap down to a reasonable temp., say about 20 degrees, and then let the evap fan come on. It prevents overloading the compressor during a high temp condition, and it also prevents circulating warm air left from the defrost cycle. I believe this device is most likely your problem. With no air circulating, the box will no cool down.. I have seen them burn and/or slhort internally. They can come apart. too. I would look here for that problem. the True manufacturing website does not give alot of info on this piece of equipment, such as a wiring diagram but manuals are available.
Check this out and let me know how it comes out.

First, please re-check to see if both fans are running, the condenser fan by the compressor and the evap fan in the freezer. Next, empty the freezer and remove the evap cover. look at the evap coils. Are they completly frosted up -- if so, you have a defrost problem - this will cause the condition you describe- IF they are not frosted, are only a few of the passes of coil frosted and some just wet with no frost? Then that means you need some freon. The fact that you have some cooling means that the compressor is probabaly OK.